We're creating a dll, written in C++, providing access to some hardware. We also have a C# program that uses this dll.
We're having an issue with the versions. Indeed, when running the C# program, it absolutely wants to use the exact C++ dll version it used when compiling. I.e. if the C# program was compiled using C++ dll 1.2.3.4, then the program will refuse to run with C++ dll 1.2.3.5.
I'd like to instruct the C# program to use any C++ dll with version 1.2.anything.
Where can I configure this in the C# project?
This question has been superseded by that one, more related to COM.
Nothing this fancy exists in C++. Using a side-by-side manifest technically permits this but you would have known about it since you would have typed the version number in the manifest of your C# program.
The far more likely explanation is that you actually created a C++/CLI assembly. Many programmers confuse C++/CLI with C++. Easy mistake since that language permits using native C++ code. But it actually gets compiled to a mixed-mode assembly, an assembly that contains both IL and native code. The normal CLR version checking occurs for such an assembly when the CLR loads it, it is only happy with an exact version match. A strong DLL Hell counter-measure.
And the normal CLR version wrangling option is available to bypass this check, a <bindingRedirect> element in your app.exe.config file. As well as controlling the assembly version number the way you do it for your C# code so this isn't necessary.
The easiest way to check if this guess is accurate is by using Project + Add Reference and select the DLL. If that doesn't draw any complaint and the assembly gets added to the References node of your C# project then you know it is a normal .NET assembly. Don't forget to take advantage of that, no pinvoke required.
Load the dll at runtime and use reflection to call it's methods.
Assembly assembly = Assembly.LoadFrom("C:\\test.dll");
Assembly.GetTypes();
Activator.CreateInstance(type);
I don't think it is possible to configure your program to use 1.2.* version and no others. Unless you would write the code for that on your own. Another possibility would be not to change the version tag of the C++ dll, but it does not seem you want to that.
A solution avoiding the version dependency would be the usage of dllimport. You can load any dll written in C++ with it. It is free of version dependency. See the example from the msdn and link at the end:
using System;
using System.Runtime.InteropServices;
class Example
{
// Use DllImport to import the Win32 MessageBox function.
[DllImport("user32.dll", CharSet = CharSet.Unicode)]
public static extern int MessageBox(IntPtr hWnd, String text, String caption, uint type);
static void Main()
{
// Call the MessageBox function using platform invoke.
MessageBox(new IntPtr(0), "Hello World!", "Hello Dialog", 0);
}
}
Description in MSDN
Related
I am aware of this similar question, but it does not respond to my problem.
I have written two .dlls using Visual Studio 2010. One is in C++, and communicates with an SDK that was written in C++. The other is a C# wrapper for that C++ library, so that it can be used in C# contexts.
My plan was that this would let me use my code in Unity3D, but apparently that is not the case. It seems like Unity3D does not allow me to import .dlls as Assets if they are not a .NET assembly. So I can add my C# wrapper, but not the C++ dll.
This results in a DllNotFoundException whenever I try to access the C++ library. I have tried simply copying the C++ library into the Assets/Plugins folder, but that gives the same results.
Is there a way to do this properly? This is a very vital part of my project setup.
The problem is that the DLL is not being found when the p/invoke runtime code calls LoadLibrary(YourNativeDllName).
You could resolve this by making sure that your DLL is on the DLL search path at the point where the first p/invoke call to it is made. For example by calling SetDllDirectory.
The solution that I personally prefer is for your managed code to p/invoke a call to LoadLibrary passing the full absolute path to the native DLL. That way when the subsequent p/invoke induced call to LoadLibrary(YourNativeDllName) is make, your native DLL is already in the process and so will be used.
internal static class NativeMethods
{
[DllImport("kernel32", SetLastError = true, CharSet = CharSet.Unicode)]
internal static extern IntPtr LoadLibrary(
string lpFileName
);
}
And then somewhere in your code:
private static IntPtr lib;
....
public static void LoadNativeDll(string FileName)
{
if (lib != IntPtr.Zero)
{
return;
}
lib = NativeMethods.LoadLibrary(FileName);
if (lib == IntPtr.Zero)
{
throw new Win32Exception();
}
}
Just make sure that you call LoadNativeDll passing the full path to the native library, before you call any of the p/invokes to that native library.
Note that the DllNotFoundException can be caused by building your Unity DLL in Debug instead of Release!
A simple oversight that can cause a headache.
This also happens when Unity can find your DLL, but is not able to find it's dependencies. Obvious fix is to place dependency DLLs into /Plugins as well, or link your dependencies statically.
Less obvious reason is when your DLL depends on Visual Studio runtime library dynamically, i.e. is built with Properties -> C/C++ -> Code Generation -> /MD option. Change it to /MT to link with runtime statically.
I'm trying to make my first c# dll.
I want to be able to call it's methods/functions from ruby with win32API.
I have made this dll:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace ClassLibrary1
{
public class Class1
{
public int PropA = 10;
public void Multiply(Int32 myFactor)
{
PropA *= myFactor;
}
}
}
I compiled it with Visual Studio 2010 and got my ClassLibrary1.dll file.
Now for the ruby part i tried this:
f = "c:/path_to_file/ClassLibrary1.dll"
mult = Win32API.new(f,"Multiply",["I"],"I")
But, i get the following error:
Error: #<RuntimeError: (eval):0:in `initialize': GetProcAddress: Multiply or MultiplyA
To be honest, I never created a dll, nor do I have experience with c#. I just wanted to get started. I have used many dll's with Ruby via win32API before (user32 mostly).
I guess my dll is not ok?
Regards,
To consume functions from DLLs as done in a Win32 context, these functions need to be export-visible from the DLL. These functions are usually flagged with dllexport and will show up in the export table of a DLL. You can verify that user32 and other Win32 DLLs do this by using a utility such as dumpbin (MSDN).
dllexport, dllimport # MSDN
Unfortunately, .NET doesn't have immediate support for making functions export-visible, only for bringing in such functions via the DllImport (MSDN) Attribute.
COM is the easiest way to consume code written within .NET from a non-.NET environment, but if you must use the lower level bindings, you can make an intermediate DLL in C, C++/CLI, or any other language and framework combination that can write export headers to a dll, to call your .NET code.
Also, A few articles exist on making this happen via post-compilation automation or other workarounds, here are a few for your reference.
How to Automate Exporting .NET Function to Unmanaged Programs # CodeProject
Unmanaged Exports # Google Sites
DllExport - Provides C-style exports for pure .NET assemblies
Without doing anything extra, the DLL created is an Assmebly intended to be run inside the .Net runtime (the CLR).
You can expose it through Com as described in the related question: Can Ruby import a .NET dll? which
Has anyone worked on calling a C# module from C module. I tried searching on internet but didn't find good examples. Though lot of sites say something like using COM interop but couldn't find a proper example or article explaining it though.
If someone can help me on this, it would be great
Thanks,
Sveerap
There is more than just COM interop if you want to call into managed code from C or C++. The are also the following lesser known methods (taken from MSDN FAQ):
How do I call a .NET assembly from native Visual C++?
There are basically four methods to
call .NET assembly from native VC++ code:
CLR Hosting API: Native VC++ module calls CLR Hosting APIs to host CLR, load and call the .NET assembly (sample code: CppHostCLR).
COM Interop: If the .NET assembly can be exposed as a COM component, native VC++ module can call into the .NET assembly through .NET – COM interop (sample code: CppCOMClient).
Reverse PInvoke: The managed code calls native code passing a delegate that the native code can call back (sample code: CSPInvokeDll).
C++/CLI: If the module containing native VC++ code is allowed to enable CLR, the native VC++ code can call
.NET assembly directly (sample code: Consuming C# Library in native C or C++ using C++/CLI)
Here is a solution. The solution allows calling a C# function from C by decorating your function with [DllExport] attribute (opposite of P/Invoke DllImport).
https://sites.google.com/site/robertgiesecke/Home/uploads/unmanagedexports
C# code
class Test
{
[DllExport("add", CallingConvention = CallingConvention.StdCall)]
public static int Add(int left, int right)
{
return left + right;
}
}
C code
int main()
{
int z = add(5,10);
printf("The solution is found!!! Z is %i",z);
return 0;
}
As #iceflow19 commented below:
The author of the link provides a CLR IL preprocessor as an added step during compilation. Since assemblies use the same binary container format (DLL) on windows, if you manually add the .Net functions offsets in IL to the vtable (the dll's list of exports), Windows is smart enough to invoke the CLR to run that code when called from C. However there is overhead. It's an unadvertised feature. This is how mixed managed libraries in C++/CLI work. To use it just add it through Nuget. The extra target added in your MSBuild project file will provide for the IL preprocessing step
You could expose your C# module as COM:
http://www.codeproject.com/KB/cs/ManagedCOM.aspx
Best method of calling managed code(c#) from unmanaged C++
http://www.codeproject.com/KB/COM/cominterop.aspx
There is also the option of building native libraries from C# code using CoreRT and call them from C.
Here is an example.
Edit: CoreRT has moved to runtimelab feature NativeAOT. Updated link.
I've been given a dll to talk to a device, I have little to no experience in C# and I'm supposed to get the device initialized by the end of the week. The dll has methods to open ports and send messages, but I have no idea how to get access to the functions
I know its a bit ridiculous to ask but im running out of time.
Thanks,
Add a Reference to the .dll file in your C# project.
Add a Using namespace at the top of whatever class is going to interact with the .dll methods.
You will now be able to access the methods.
Edit: If your library is unmanaged you'll have to use Pinvoke.
Generally speaking, a feature to call from managed code into unmanaged code (which I assume your DLL is) is called P/Invoke and generally involves annotating required static extern methods with attributes.
Add a reference to the dll in your project (selet browse to find it) and you should be able to access the functions within. As for how to make your device work with it, I think you're on your own :)
If the DLL is a .Net assembly, you can load it into a Visual Studio project by adding it as a reference.
In the absence of documentation, it can also be extremely helpful to load the assembly into .Net Reflector, which lets you inspect the guts of the assembly, even to the point of disassembling the code inside the methods.
1- If it is managed Dll , i.e. Written using .net framework than calling a method from the dll is like you are calling a method from your own class.
just add the reference of the dll in your project and include the namespace reference by 'Using' keyword.
2- If it is not than you need to import your dll dynamically, you can use [DllImport]
I am wrote a visual c++ win32 console app, and i wrote it and tested it in
win32 console project
. then i switch to
win32 project
and imported all the source files and created a dll for it. by mark the class i want to export as
#define DllExport __declspec( dllexport )
class DllExport theClass {
}
it works and the dll is generated. then i created a another c# project and want to add the dll to the project. by reference->add reference-> browser. then i select that dll.
then it is gives me an error
a reference to the '''''''.dll could
not be added. please make sure that
the file is accessible, and that is a
valid assembly or com component.
anyone knows where i did wrong to generate/import the dll?
thanks
The Add Reference dialog can only work for DLLs that contain metadata (managed code) or a type library (a COM server). Your DLL doesn't fit that bill, you can only use the [DllImport] attribute in C# code to use the P/Invoke marshaller to call an unmanaged DLL entrypoint.
That can not be a native C++ class, like you are trying to do, there is no reliable mechanism for managed code to allocate unmanaged memory and call the constructor (and destructor) of a native C++ class. Short from the difficulty of finding the constructor and destructor code, there is no way for the P/Invoke marshaller to know the size of the object. The C++ language doesn't generate the metadata necessary to know this required information.
If you want to pursue P/Invoke then write an plain global function, decorated with extern "C", __declspec(dllexport) and (optionally) __stdcall.
If you want to export a C++ class then the only avenue is using the C++/CLI language and write a "ref class" wrapper for the native C++ class.
Or you could write a COM coclass, the universal glue in Windows. Very well supported by .NET, probably not something you want to pursue if you never wrote COM code before. ATL is the best way to get one going.